Some contemporary communication systems use the Internet for transmitting voice calls; the underlying technology is generally referred to as voice over internet protocol, or VoIP. Gateways are devices often used in VoIP systems to bridge the traffic across domains. For example, a business using an internet protocol-based private branch exchange (IP-PBX) system usually has one or more VoIP gateways to connect the PBX to the public internet, and also may have some ‘PSTN gateways’ for connecting to the traditional public switched telephone network. The gateways are responsible for relaying control signals as well as for relaying the media for each communication link.
Currently, gateways are tested for their quality with respect to relaying audio streams by having a human tester listen in on VoIP calls. In general, any echo and interference (distortion) are noted by the tester. However, such a testing process is somewhat subjective, is not scalable to testing large numbers of devices, and can be quite expensive.